The present invention involves the reproduction of sound, typically voice and music, in an enclosed space. Systems such as the type disclosed herein have been adopted by music lovers for the reproduction of stereophonic high fidelity sources either in the form of two channel audio or multi channel audio-video home entertainment systems.
As noted above, applicant has previously filed applications directed to loudspeaker systems of the type disclosed and claimed herein. These generally involve arrays of individual loudspeakers or transducers in one or more straight-line arrangements, so-called line-arrays. It was the domain of the previously filed applications to teach the use of a multitude of drivers or transducers in an organized way to eliminate the normally encountered limitations of frequency selective dispersion of sound and to improve the dynamic range of such loudspeakers intended for residential use.
To further characterize applicant's prior applications, transducers were taught as being configured into vertical lines on a face of a tall, slim cabinet. Ideally, two vertical arrays in each cabinet were employed, one consisting of mid-range drivers and the other consisting of high-frequency drivers, commonly referred to as tweeters, parallel thereto. In a typical 2-channel system, the cabinets are used in pairs with the lines of drivers arranged in mirror-image such that the tweeter lines are physically placed toward the center of the listening space with the mid-range drivers on the outside of that space. Obviously, these speakers could also include a line array in a horizontal orientation between the left and right-hand speakers in order to support a center channel placed proximate to a video display to create a home theater system.
Whether one employs speaker systems for 2-channel stereophonic reproduction or multi-channel home theater systems, there are advantages inherent in the use of line arrays of transducers rather than point source drivers common to the prior art. Point source transducers are oftentimes employed because it is relatively easy to measure the output of a point source. A measuring microphone is also an approximation to a geometric point. The principle reciprocity makes it easier to measure a point with a point. However, this has virtually no relevance to the way humans hear music.
Although line arrays are difficult to measure, and when measured in conventional ways, yields results which may be difficult to interpret, there are certainly advantages in reproducing music using line arrays of transducers. Measuring difficulties are expected from the placement of mid-range and tweeter line arrays side-by-side which can cause aberrations of dispersion of sound, known as polar errors, in the horizontal plane in the cross-over region where both lines are operating. However, it has been observed that this does not occur. This expectation arises from point-source thinking; that is, if the line is viewed in horizontal cross-section, it appears to be two point sources side-by-side. Such a configuration would indeed produce horizontal polar errors. But line arrays cannot be analyzed in this manner because it would only be valid for the plane of the cross-section. The sources are physically extensive in the vertical direction and any movement out of the plane of the cross-section mentioned above yields a different polar summation. In fact, it is not possible to physically observe only the plane of the cross-section as a plane is a mathematical abstraction. Any spatial averaging in the observation causes the expected polar aberrations to be unobservable. Looked at differently, in normal human hearing, there are three mechanisms of spatial averaging. First, observers have two ears which are separated from each other in space. Second, ears collect sounds over the area of the outer ear which is not a point. Third, when one listens to an audio system, his or her head continually makes small movements which continually reposition the ears in space. As such, in human hearing, there is both static and dynamic spatial averaging occurring simultaneously and continuously.
It is also noted that point source transducers radiate a spherical wave, that is, one which is isotropic whereas a line source radiates a cylindrical wave, that is, the wave is anisotropic. The sound pressure from a point source decreases as the square of the distance from the transducer where the sound pressure for a line source decreases linearly with distance. This can be explained by noting that the area of a spheric surface is proportional to its radius squared, while the area of a cylinder is proportional to its radius. From a practical standpoint, this is significant for in stereophonic listening from point sources, it is important to listen precisely in the middle, or equal distance between the two loudspeakers because the square law sound pressure relationship means that if the listener moves off center, the central auditory image is affected by a square of the distance providing the listener with a sense that he or she has “fallen into” the nearer loudspeaker. With a line array speaker system, this effect is reduced by an order of magnitude resulting in a much larger usable listening area.
Yet a further advantage in employing a line array of transducers in a speaker system involves the “aperture” of the line or in other words, the height of the cylindrical wave. This height is approximately equal to the physical length of the line array. In a typical residential listening environment, this means that reflections from the ceiling are minimized. This is important because overhead reflections can cause auditory backward inhibition in normal human hearing. This prevents a sense of “envelopment” in the reproduced sound. By reducing the cause of auditory backward inhibition, line arrays are able to produce a much more involving psychoacoustic effect. By contrast, a point source is a relatively small creator of acoustic energy which disperses sound waves broadly. As such, the line array is the only direct radiator configuration which can simultaneously limit dispersion in one direction (vertical) while maximizing it in another (horizontal). However, this can only be achieved if the entire structure can be made narrow, the geometry of such a structure being a cornerstone of the present invention.
It is thus an object of the present invention to provide a speaker system possessing a linear array of transducers which optimizes the interaction between the loudspeaker, the room and one or more listeners.
This and further objects will be more readily apparent when considering the following disclosure and appended drawings.